We are excited to offer two types of redundant storage for Windows Azure: Locally Redundant Storage and Geo Redundant Storage.
Locally Redundant Storage (LRS) provides highly durable and available storage within a single location (sub region). We maintain an equivalent of 3 copies (replicas) of your data within the primary location as described in our SOSP paper; this ensures that we can recover from common failures (disk, node, rack) without impacting your storage account’s availability and durability. All storage writes are performed synchronously across three replicas in three separate fault domains before success is returned back to the client. If there was a major data center disaster, where part of a data center was lost, we would contact customers about potential data loss for Locally Redundant Storage using the customer’s subscription contact information.
Geo Redundant Storage (GRS) provides our highest level of durability by additionally storing your data in a second location (sub region) within the same region hundreds of miles away from the primary location. All Windows Azure Blob and Table data is geo-replicated, but Queue data is not geo-replicated at this time. With Geo Redundant Storage we maintain 3 copies (replicas) of your data in both the primary location and in the secondary location. This ensures that each data center can recover from common failures on its own and also provides a geo-replicated copy of the data in case of a major disaster. As in LRS, data updates are committed to the primary location before success is returned back to the client. Once this is completed, with GRS these updates are asynchronously geo-replicated to the secondary location. For more information about geo replication, please see Introducing Geo-Replication for Windows Azure.
Geo Redundant Storage is enabled by default for all existing storage accounts in production today. You can choose to disable this by turning off geo-replication in the Windows Azure portal for your accounts. You can also configure your redundant storage option when you create a new account via the Windows Azure Portal.
Pricing Details: The default storage is Geo Redundant Storage, and its current pricing does not change. The current price of GRS is the same as it was before the announced pricing change. With these changes, we are pleased to announce that Locally Redundant Storage is offered at a discounted price (23% to 34% depending upon how much data is stored) relative to the price of GRS. Note if you have turned off geo-replication and choose to enable geo-replication at a later time, this action will incur a one-time bandwidth charge to bootstrap your data from the primary to its secondary location. The amount of bandwidth charged for this bootstrap will be equal to the amount of data in your storage account at the time of bootstrap. The price of the bandwidth for the bootstrap is the egress (outbound data transfer) rates for the region (zone) your storage account is in. After the boostrap is done, there are no additional bandwidth charges to geo-replicate your data from the primary to the secondary. Also, if you use GRS from the start for your storage account, there is no boostrap bandwidth charge. For full details, please review the pricing details.
Some customers may choose Locally Redundant Storage for storage that does not require the additional durability of Geo Redundant Storage and want to benefit from the discounted price. This data typically falls into the categories of (a) non-critical or temporary data (such as logs), or (b) data that can be recreated if it is ever lost from sources stored elsewhere. An example of the latter is encoded media files that could be recreated from the golden bits stored in another Windows Azure Storage account that uses Geo Redundant Storage. In addition, some companies have geographical restrictions about what countries their data can be stored in, and choosing Locally Redundant Storage ensures that the data is only stored in the location chosen for the storage account (details on where data is replicated for Geo Redundant Storage can be found here).
Monilee Atkinson and Brad Calder